The La Salle County Health Department confirmed that mosquitoes collected in Dayton and Naplate tested positive for West Nile virus, officials said.

The mosquitoes were trapped on Sept. 16 and 17, and Environmental Health staff conducted confirmatory testing at the health department. Late summer and early fall typically see an increase in West Nile virus activity.

To date in 2025, mosquitoes testing positive for West Nile virus have been found in several La Salle County communities, including Marseilles, La Salle, Ottawa, Oglesby, Streator, Seneca, Dayton and Naplate.

West Nile virus spreads through the bite of infected Culex mosquitoes, commonly known as house mosquitoes. Symptoms can include fever, nausea, headache, and muscle aches, lasting from days to weeks. Most infected people do not show symptoms, but severe illness such as paralysis, meningitis, or encephalitis can occur, especially in people over 60 or those with weakened immune systems.

The Illinois Department of Public Health urges residents to “Fight the Bite” by following three steps: reduce mosquito breeding sites, use insect repellent, and report standing water.

Residents should ensure doors and windows have tight-fitting screens, eliminate standing water where mosquitoes breed, wear protective clothing outdoors, and use EPA-approved insect repellents containing DEET or other effective ingredients.

Stagnant water sites such as roadside ditches or flooded yards should be reported to local authorities, who may apply larvicide to control mosquito larvae.

For a full list of West Nile virus activity in LaSalle County, visit www.lasallecountyil.gov under Environmental Health/Vector Control. Statewide information is available at the Illinois Department of Public Health website: https://dph.illinois.gov/topics-services/diseases-and-conditions/west-nile-virus.